Generally, dozing operation with a bulldozer is carried out under manual control by the operator. A typical manual operation by the operator involves, blade raising, blade lowering, tilting and pitching. In such operation, the operator controls the load on the blade caused by digging and carrying to be constant while avoiding a running slip (shoe slip) of the vehicle body. Load dumping is carried out such that the operator raises the blade with the captured soil therein and allows the blade to pitch so that the blade is emptied to mound the soil (mounding). In the case of dumping soil, for instance, from a cliff (dropping), the operator operates the blade so as to be pushed horizontally, with the cutting edge of the blade kept in a certain position relative to the ground.
Such manual operation not only requires operator's skill and experience but also involves frequent manipulation of the blade and other members, so that the operator gets tremendous fatigue, no matter how skillful he is. To automate dozing operation to solve this problem, several automatic blade control techniques for bulldozers have been, up to now, proposed and put to practical use.
One such automatic control technique for load dumping is proposed by the applicant of the present invention and disclosed in Japanese Patent Publication (KOKAI) Gazette No. 7-26586 (1995). The automatic dozing control system for a bulldozer disclosed in this publication comprises a laser beam receiving sensor mounted on the bulldozer and a laser beam projector located at a digging completion point (dumping point) on the ground. Upon detection of the arrival of the bulldozer at the dumping point by means of the laser beam receiving sensor and the laser beam projector, the transmission is automatically shifted from forward gear into reverse gear.
As mentioned earlier, load dumping dependent on manual operation causes tremendous fatigue to the operator and cannot provide smooth load dumping. The publication No. 7-26586 only teaches shifting of the transmission between forward gear and reverse gear upon the arrival of the bulldozer at the dumping point, but does not disclose the control of the blade to dump soil.
The present invention is directed to overcoming the above problems and the prime object of the invention is therefore to provide a dozing system for a bulldozer, which is capable of automating a dumping process to smoothly and effectively dump the contents of the blade.